Die for hydrostatic extrusion of sections having elongated projections

ABSTRACT

In the hydrostatic extrusion of rods having ribs extending from a core part, extending longitudinally or helically, a billet is hydrostatically extruded through a die having grooves which decrease in width from the inlet die towards the smallest crosssection of the die opening, so that the grooves are filled with the material of the billet.

llnited States Patent 1 Nilsson Oct. 16, 1973 DIE FOR HYDROSTATIC EXTRUSION OF SECTIONS HAVING ELONGATED PROJECTIONS [75] Inventor: Jan Nilsson, Robertsfors, Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden 22 Filed: Mar. 1, 1972 [21] Appl. No.: 230,816 '30] Foreign Application Priority [i515 March 19,1971 Sweden ..3545/1971 [52] US. Cl. 72/467 [51] Int. Cl. B21c 25/02 [58] Field of Search 72/467, 60, 253, 72/260, 258

[56] References Cited UNITED STATES PATENTS 3,267,7l2 8/1966 Atkin 72/260 3,583,204 6/1971 Nilsson 72/467 OTHER PUBLICATIONS High Pressure Forming by R. Khol; pp. 124-130 of Machine Design; Jan. 9, 1969 Primary Examiner-Richard J. Herbst Attorney-Jennings Bailey, Jr.

[5 7] ABSTRACT In the hydrostatic extrusion of rods having ribs extending from a core part, extending longitudinally or helically, a billet is hydrostatically extruded through a die having grooves which decrease in width from the inlet die towards the smallest cross-section of the die opening, so that the grooves are filled with the material of the billet.

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Q PATENTEI] OCT 1 6|975 SHEET E OF 6 DIE FOR HYDROSTATIC EXTRUSION OF SECTIONS HAVING ELONGATED PROJECTIONS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die for manufacturing sections having longitudinal projections by means of hydrostatic extrusion of a billet through a die orifice of the desired cross section. The projections may be parallel with the section or helical in shape. As examples of products which can be manufactured may be mentioned shafts having splines, toothed gears having straight or oblique teeth, pump rotors, etc.

2. Prior Art One problem in the hydrostatic extrusion of sections having elongated projections with grooves between them is to get the billet material to completely fill the grooves in the die which form the ridges along the section so that the projections acquire the intended crosssection and shape. This difficulty is particularly pro nounced when the elongated projections are also rather high. Consequently, variations in measurements of the product produced have been considerable. The reason that the billet material does not completely fill out the grooves in the die which are to form the elongated projections is that between the cross-section of the die where the orifice is largest, i.e. the transition between a conical inlet area and the bottom of the grooves forming the projections and the smallest cross-section of the die orifice there is an extreme elongation of the central part of the billet, which causes the part of the projection formed to stretch so that the height and width decrease if the radial displacement of the billet material is insufficient.

SUMMARY OF THE INVENTION The invention provides a solution to the abovementioned problem of completely filling the grooves of the die which are to form the elongated projections and thus obtaining the correct measurements for the extruded section. It is characterised in that the grooves in the die to produce the elongated projections on the rod are shaped so that their width decreases from the inlet side towards the smallest cross-section of the die opening. A tangential decrease in dimensions is thus obtained, which gives successive tangential compensation for the extension of the projections as the material is extended in the central part of the billet. In dies for extruding sections having helical projections it may be suitable or necessary to have a smaller pitch in the first part of the die groove, i.e. the part of the groove lying ahead of the smallest cross-section of the die orifice. In certain cases it may also be necessary or suitable to allow the pitch of the die groove to deviate somewhat from the pitch of the elongated projections in order to obtain the desired pitch. In one embodiment the projections between the grooves of the die are bevelled in the area immediately before the smallest cross-section of the die orifice so that the stresses in the projections between the grooves of the die can be decreased somewhat, thus decreasing the risk of rupture.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further exemplified with the help of the accompanying drawings.

FIGS. 1 and 2 show two examples of rod shaped products manufactured in dies according to the invention,

FIG. 3 a section of a die previously used together with a billet and a product in the die,

FIG. 4 a view of the die according to FIG. 3 from the inlet side,

FIG. 5 a corresponding view of a die for extruding a section having the same cross-section but with the elongated projections running helically,

FIG. 6 a section extruded in a die of previously known type showing how the measurements of this section differ from the cross-section of the die,

FIG. 7 a die having tagential compensation in the grooves which are to form the ridge,

FIG. 8 a view of the die according to FIG. 11 from the inlet side,

FIG. 9 a section through a rod produced in the die,

FIG. 10 a section through a die for producing a section having helical elongated projections,

FIG. 11 a view from the inlet side of the die accord- DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a shaft having elongated projections 1 like splines around a core part 2. The projections 1 are parallel to the shaft itself. FIG. 2 shows a section having helically arranged projections 3 around a core part 4. The projections are shaped so that the section can be used as a rotor in a compressor. The die in FIGS. 3, 4 and 5 is of a type already known. It has a conical inlet part 6 and an opening 7 with grooves 8 and projections 9 between the grooves in order to produce the bar 10 shown in FIG. 6 which consists of a core part 11 and elongated projections 12 projecting from this core. In FIG. 6 the profile of the die is shown by broken lines 13. A billet 14 is shown in the die, and this is shaped to the section 10. The edges of the die hidden by the billet 14 are shown in broken lines. In dies for producing sections having straight projections l, 12 the sides of the grooves 8 are parallel to the longitudinal axis of the die, as shown in FIGS. 3 and 4. In dies according to FIG. 5 for producing sections having projections 3, 12 running helically, the base of the groove is at a constant distance from the longitudinal axis of the die and the side surfaces of the groove form the same angle to the longitudinal axis of the die along the whole length of the groove. To shape the billet 14 the cross section is decreased uniformly in the conical inlet part 6 of the die from the diameter D, to the diameter D which corresponds to the greatest measurement of the die opening, therefore within the vertical section A. Within the vertical section B the material is shaped to the section 10 with the core 11 having diameter D; and projections 12. Even in the upper part of section B the outermost part of the projections 12 are already properly formed. When the cross section within the section B in the die is reduced, an extension is obtained. Even the outermost, finished parts of the projections must be extended to the same extent as the rest of the material. In order to obtain a complete cross-section in spite of the extension, a radial material flux is required within the section B to keep the die groove 8 filled. However, in many cases it has been found that this material flux is insufficient and the cross section of the projections 12 is less than the cross section of the grooves 8. As shown in FIG. 6, the tops of the projections have the width H instead of the same width C as the groove 8. Measured across the projections the dimension of the section will be D 2.4 D;, and not equal to the measurement D between the bases of two grooves 8. The width of the projections at the tops will be C 2K H and will gradually increase to C towards the base of the projection on the section. The rod will therefore not have the same dimensions as the die opening.

FIGS. 7 and 8 show a method of shaping the die so that a rod having the same cross section as that of the die opening is obtained, for example a rod according to FIG. 9 with four longitudinal ridges 12 about a core 11. In this embodiment the bases of the grooves 8 are parallel to the longitudinal axis of the die 5, whereas the sides 16a, 16b are inclined with respect to this axis in the area F above, so that the width of the groove decreases in the direction of extrusion. In the section F, material is forced tangentially in towards the centre of the groove and compensation is therefore obtained for the alteration in dimensions which is otherwise obtained when the elongated projections are extended. This may be called tangential compensation.

FIGS. 10 and 11 show a die according to FIGS. 7 and 8 modified to produce a section having four helically arranged elongated projections.

FIGS. 12 and 13 shown a die according to FIGS. 7

and 8 which is modified in such a way that the projection 9 between the grooves of the die is somewhat bevelled at the transition from the conical surface of the die to its vertical orifice surface. The projection 9 will therefore acquire a surface 19 which will form a more acute angle with respect to the axis of the die than the conical inlet surface 6. i

The die according to the invention is applicable to all types of sections. That a die has been described which produces a section having only four elongated projections with flat sides is purely because the invention can be more clearly explained in this way.

I claim:

1. Die having an extrusion orifice with a substantially circular opening and grooves communicating therewith for producing rods having elongated projections extending from a central core part, by means of hydrostatic extrusion, the grooves in the die decreasing in width from the inlet side towards the smallest crosssection of the die opening.

2. Die according to claim 1, in which the grooves are helical in shape.

3. Die according to claim 1 having a conical inlet,in which the projections between the grooves of the die are bevelled nearest to the smallest cross-section of the die so that the surfaces of the projections of the die between the grooves are directed towards the center of the die from a more acute angle to the longitudinal axis of the die than the conical surface of the inlet. 

1. Die having an extrusion orifice with a substantially circular opening and grooves communicating therewith for producing rods having elongated projections extending from a central core part, by means of hydrostatic extrusion, the grooves in the die decreasing in width from the inlet side towards the smallest cross-section of the die opening.
 2. Die according to claim 1, in which the grooves are helical in shape.
 3. Die according to claim 1 having a conical inlet,in which the projections between the grooves of the die are bevelled nearest to the smallest cross-section of the die so that the surfaces of the projections of the die between the grooves are directed towards the center of the die from a more acute angle to the longitudinal axis of the die than the conical surface of the inlet. 